I. Field of the Invention
This invention relates to a process of producing 2-(4'-hydroxyphenoxy)-3-chloro-5-trifluoromethylpyridine. 2-(4'-hydroxyphenoxy)-3-chloro-5-trifluoromethylpyridine is an important compound as an intermediate in the production of pharmaceuticals and agricultural chemicals.
II. Description of the Related Art
A process of producing 2-(4'-hydroxyphenoxy)-3-chloro-5-trifluoromethylpyridine is known in which hydroquinone, 2,3-dichloro-5-trifluoromethylpyridine and potassium hydroxide are reacted in dimethylsulfoxide as a solvent under nitrogen atmosphere under stirring at 150.degree. C. for 2 hours, the resulting mixture is allowed to cool and neutralized with hydrochloric acid, the resultant is extracted with methylene chloride, and the obtained extract is dried and condensed to obtain the desired product (Japanese Laid Open Patent Application (Kokai) No. 61182/79).
However, in this process, the yield of the product is low because of the influence of water produced as a byproduct by the reaction of hydroquinone and potassium hydroxide. Further, the operations for carrying out the process are complicated. Thus, although this process may be suited for the production in laboratory scale, it is not suited for industrial scale production.
Also known is a process of producing 2-(4'-hydroxyphenoxy)-3-chloro-5-trifluoromethylpyridine in which hydroquinone is dissolved in a polar solvent, the obtained solution is degassed under heat under low vacuum, aqueous sodium hydroxide or potassium hydroxide is added to the solution in the amount sufficient to neutralize 75 -100% of hydroquinone, the resulting mixture is heated under low vacuum so as to distill water until the residual water content is reduced to not more than 1% by weight of the solvent and the reactants, the vacuum is released with a dry inert gas, and the resultant is cooled and reacted with 2,3-dichloro-5-trifluoromethylpyridine to obtain the desired product with high yield (Japanese Laid Open Patent Application (Kokai) No. 962/83).
However, in this method, removal of the water dissolved in the polar aprotic solvent and the water produced as a byproduct is extremely difficult, so that complicated operations are necessary to reduce the water content to the level not adversely affecting the reaction. Further, it is necessary to distill off water under low vacuum, which is troublesome.
Still another process of producing 2-(4'-hydroxyphenoxy)-3-chloro-5-trifluoromethylpyridine is known, in which 2,3-dichloro-5-trifluoromethylpyridine and 4-methoxyphenol are reacted in dimethylsulfoxide at 80.degree.-85.degree. C. and the obtained 2-(4'-methoxyphenoxy)-3-chloro-5-trifluoromethylpyridine is demethylated with 48% aqueous hydrobromic acid solution t obtain the desired product (Japanese Patent Publication (Kokoku) No. 44747/88).
However, this process cannot be carried out in one pot, so that it is not suited for industrial scale production.